Precision, Accuracy Measurements, Units, Scientific Notation

Transcription

1 Precision, Accuracy Measurements, Units, Scientific Notation

2 DIMENSIONAL ANALYSIS It is a technique used in chemistry to give precise and accurate values.

3 I. Accuracy and Precision Accuracy how close a measurement is to the actual (target) value Precision How close different measurements are to one another OR the degree to which a piece of equipment can accurately measure. It is best practice to use the most precise piece of equipment available All measurements must be reported with the correct accuracy

4 II. Measurements Measurements can be either Qualitative or Quantitative Qualitative Quality, like a color or smell, are simple observations Quantitative Quantity, meaning numeric We will focus more on the Quantitative measurements in this course. All quantitative measurements need to have a number and a unit A number without a unit has no standing.(means nothing)

5 III. Units Definite quantity used as a standard for a measurement There are three Basic Units - Length meters (m) mass grams (g) (amount of matter, stuff ) volume liters (L) (3-D space, also m 3 ) But Sometimes these aren t be best way to represent a quantitative measurement Many of our measurements will be multiples of these standards There are two ways scientists commonly deal with multiples Unit Prefixes Scientific Notation

6 IV. Scientific Notation The other way to illustrate multiples of very large or small numbers is to use Scientific Notation Most chemistry teachers will tell you a number we use quite often is 602,200,000,000,000,000,000,000 Which is a pain to write out over and over again, so it is commonly condensed using scientific notation, which shows its power of x10 23

7 IV. Scientific Notation For numbers larger than one: 1. Find the decimal point If none is present, we assume it is at the end 23,000, Move it to the left until it s behind the last number Erase any zeroes on the right Add 10 n where n is the number of spaces you moved the decimal

8 IV. Scientific Notation For numbers smaller than one: 5. Move the decimal to the right until it s behind the first non-zero number Erase any zeroes on the left Add 10 n where n is the number of spaces you moved the decimal

9 V. Prefixed Units We will commonly use prefixed units like milliliters (ml) and centimeters (cm) so it is best to know how to use the chart and convert between prefixed units Ex. #1: How many micrograms (μg) are in grams? 12,250,000 μg Ex. #2: How many nanoliters (nl) are in 33 centiliters (cl)? 330,000,000 nl Ex. #1: How many cubic millimeters are in 1 cubic meter? 1,000,000,000 mm 3 mm mm mm

10 V. Prefixed Units There are many prefixes for the Metric (SI) system Prefix Symbol Multiplier Exponential yotta Y 1,000,000,000,000,000,000,000, zetta Z 1,000,000,000,000,000,000, exa E 1,000,000,000,000,000, peta P 1,000,000,000,000, tera T 1,000,000,000, giga G 1,000,000, mega M 1,000, Please Fill in the Bold rows. kilo k 1, hecto h deca da

11 V. Prefixed Units Prefix Symbol Multiplier Exponential deci d centi c milli m micro µ nano n pico p femto f atto a zepto z yocto y

12 VI. Significant Figures Significant Figures or SigFigs are used to reflect how accurate a measurement was. When making a measurement, we use a digit for all possible measurements and one digit for an estimate all possible measurements means each size of line or graduation

13 VI. Significant Figures Summary

14 VI. Significant Figures I is important to use your measuring tool correctly and report the number to the correct place. If you round a measurement, it may be interpreted as a less precise, and possibly a less accurate, measurement. When looking at a measurement you did not make, we can count the number of significant figures to make a determination about the precision of the tool the researcher used

15 VII. Rules of Graphing 1. All graphs are made with a ruler 2. All graphs are approximately of a ½ page size on a graph paper 3. All graphs have a descriptive title (more than just apples vs. oranges) 4. All graphs have x and y labels including units (mg, sec, years, Celsius, etc.) 5. Axis increments a. have to be even in distance and value (i.e. 5, 10, 15, 20) b. do not have to start at zero (find appropriate range)

16 VII. Rules for Graphing continued 6. Multiple data sets that belong together and are compared need to be graphed together and either have different colors or lines indicated by a key! 7. Data points contain an x and y value (x, y) 8. The independent variable (the variable that is manipulated in an experiment) will be graphed on the x-axis Note: time is mostly on the x axis what you change is the time when measurements are taken! but in some labs you will measure the time it takes for some reactions (Rx) to happen. Then time is a dependent variable (example: enzymes). 9. Dependent variable is the variable that changes due to the manipulation of the independent variable and will be graphed on the y-axis

17 VII. Rules for Graphing continued 10. Choose appropriate graphs unless there are specific instructions. Choices are a line or bar graph 11. Connecting data points can be either point-to-point or best fit lines Failure to meet all requirements will result in a deduction of points in lab reports!

18 Sample Data Table & Graph Graph the given data. Date(Day) Temperature ( 0 C)